I think the spectrum is huge. I've heard that some researchings think the spectrum is

ADD/ADHD > Depresion > Bipolar II > Bipolar I > Schizoaffective > Schizophrenia

There is a huge difference between ADD and schizophrenia.... o.O

Plus not everyone has all the symptoms. I'm not such a huge risk taker, for example. I've never been in the hospital although I think there are times I should have been. My psychologist told me that some people only have one manic episode in their lifetime and the rest is depression. So.... yeah, there is a huge difference and although we're all the same we're all extremely different. I think that's why it is so hard to treat.